This invention relates to an HF broadband amplifier switchable by means of an external control command between amplification and attenuation and including a differential amplifier input stage, and a voltage divider for setting the potential at the differential amplifier.
An RC element is usually arranged in a broadband amplifier, this RC element determining the lower limit frequency of the amplifier. If a surge occurs in the potential at the amplifier output when switching the amplifier on or off, then this surge in potential must be compensated for initially via the capacitor of the RC element and this leads to relatively long and very often undesirable switchover times. Previously it was to prevent these large changes in potential at the output connection of the amplifier. A four quadrant multiplier may be used for example to achieve this.
However, as will be seen later, such a circuit suffers from serious difficulties when it is desired to produce it as an integrated circuit due to the inherent capacitance of integrated circuit transistors which make it impossible to apply this circuit to integrated technology.